The present invention relates to a rotating electric machine having a rotor and a stator opposing the rotor and having a stator coil end, and a cooling system for the rotating electric machine.
A rotating electric machine for a vehicle motor or the like known conventionally in the related art includes a stator and a rotor. As the stator which constitutes the rotating electric machine, a stator as shown in FIG. 8 is conceived in the related art. FIG. 8 is a schematic perspective view of a first example of the stator which is conceived in the related art. A stator 10 shown in FIG. 8 includes teeth 14 projecting in the radial direction on an inner peripheral surface of a stator core 12, which is configured with a laminated steel plate or the like, at a plurality of positions in the circumferential direction, and coils 16 are wound around the teeth 14 in the concentrated winding manner. Coil end bodies 18 which are coil portions projecting in the axial direction from axial both end surfaces of the stator core 12 and constitute stator coil ends are designed to be stiffened by being dipped in or painted with varnish. The coil end bodies 18 are stiffened in order to secure insulating properties between the coils 16 in respective phases, and to provide sufficient mechanical strength to the coil end bodies 18.
Mounting portions 20 for fixing the stator 10 in a motor case (not shown) are provided on an outer peripheral surface of the stator core 12 at a plurality of positions in the circumferential direction. Although it is not shown in the drawing, lead wires connected to the each coil 16 are drawn from part of the coil end body 18, so that the lead wires are connectable to an inverter (not shown) or the like as an outer circuit. Although in the configuration shown in FIG. 8 the each coil 16 is wound around the teeth 14 in the concentrated winding manner, winding the coil 16 so as to straddle a plurality of the teeth 14, in so called “distributed winding manner” may also be employed.
FIG. 9 is a schematic perspective view of a second example of the stator conceived in the related art. FIG. 10 is a side view of the stator shown in FIG. 9, while FIG. 11 shows the right side of the stator of FIG. 10. A stator 22 shown in FIGS. 9 to 11 is configured in such a manner that a pair of the coil end bodies 18 (see FIG. 8) projecting in the axial direction from both axial end surfaces of the stator core 12 at axial end portions of the coils 16 (see FIG. 8) wound around the teeth 14 (see FIG. 8) are embedded in resin, that is, resin molded, so that a pair of resin mold coil ends 24, which are a pair of the stator coil ends, are formed. Employing the resin mold coil ends 24 as the stator coil ends makes it possible to reduce the cost of manufacturing the rotating electric machines and to improve the overall heat discharge properties of the coil end bodies 18 when the stator coil ends are cooled using oil or the like. In this example, the configuration is otherwise the same as that of the first example of the stator shown in FIG. 8 described above.
The rotating electric machine including the stator 22 as described above is cooled in the following manner. FIG. 12 is a schematic diagram showing an example of a cooling system 26 for the rotating electric machine according to a related art, and includes the stator 22 shown in FIGS. 9 to 11. The cooling system 26 includes a motor 28 as the rotating electric machine and an oil circulation path 30. The motor 28 includes the stator 22 fixed to an inner side of a cylindrical housing 32 and a rotor 34. A pair of metallic covers 36 are fixed to axial both end portions of the metallic housing 32. Each of the covers 36 includes a hole portion 38 at a center portion thereof, and is provided with a bearing 40 in the hole portion 38. It is also possible to additionally provide inside each hole portion 38 with a sealing member for preventing cooling oil from leaking from the interior of the cover 36. The rotor 34 is radially opposed to an inner peripheral side of the stator 22 in a state of being fixed to an outer peripheral side of a mid portion of a rotary shaft 42. The rotary shaft 42 is supported by the bearings 40 so as to be rotatable with respect to the covers 36. The pair of covers 36 and the housing 32 constitute a motor case 44.
The motor case 44 is provided with a cooling oil supply port 46 and a cooling oil discharge port 48. The cooling oil supply port 46 and the cooling oil discharge port 48 are connected to the oil circulation path 30, which is further provided with an oil pump 50. The cooling oil discharged from the oil pump 50 is supplied from the cooling oil supply port 46 into the motor case 44, in which it flows downward in the direction of gravity. The cooling oil flows downward through a gap between an inner surface of the motor case 44 and the resin mold coil end 24 and is fed from the cooling oil discharge port 48 to the oil circulation path 30 and is accumulated in an oil pan 52, from which it is drawn into the oil circulation path 30 by the oil pump 50. In such a rotating electric machine cooling system 26, even when the coils 16 (see FIG. 8) which constitute the motor generate heat during operation, the generated heat may be transferred from the coil end bodies 18 (see FIG. 8) to the motor case 44 via the cooling oil, so that the motor 28 can be cooled.
Also, Japanese Patent Publication JP-A-2000-228843 discloses a motor having a stator formed integrally with a housing, a rotor being formed integrally with a rotary shaft, and brackets configured to support the rotary shaft and arranged at both ends in a motor axis direction, in which rib-shaped projections are provided in the radial direction at positions inside the brackets corresponding to gaps formed between adjacent coil ends. This publication describes that, in a motor according to the disclosed configuration, heat discharging paths for transferring heat generated from the coil ends to the brackets via the projections are secured, so that heat discharging properties are enhanced.
Additionally, Japanese Patent Publication JP-A-2005-73351 discloses a rotating electric machine configured in such a manner that a hollow portion in a inner hollow shaft constituting a rotary shaft is connected to an oil pump, cooling oil is supplied to the hollow portion and sprayed inside the housing via openings formed on a outer hollow shaft which is disposed outside the inner hollow shaft and constitutes the rotary shaft whit the inner hollow shaft, and a cooling oil holding member is provided in the housing. The cooling oil holding member employed in that configuration has a recessed shape opening in the direction toward the rotary shaft so as to surround a stator coil end on an outer peripheral side thereof. This publication describes that this configuration enables the cooling oil holding member to sufficiently cool the stator coil end, the stator coil, and the stator with the cooling oil.
Japanese Patent Publication JP-A-2005-354821 discloses a motor configured in such a manner that a winding migrating portion of stator winding is coated with a molded resin, an annular-shaped notched portion is formed in the vicinity of a connecting portion with respect to an end surface of a stator on an outer peripheral surface of the resin molded portion, a coolant flow channel which surrounds the periphery by the notched portion, an end surface of the stator in a motor axis direction and an inner peripheral surface of a housing is defined, and coolant circulated in the coolant flow channel is discharged out from a coolant discharging hole penetrated through the resin molded portion.
Furthermore, Japanese Patent Publication JP-A1-2004/19468 discloses a motor in which both end surfaces of a coil and a stator core of a stator unit are covered by a coil end cover having a square C-shape, the coil end cover being formed with a cooling oil inlet port on a lower portion thereof and a cooling oil discharge port on an upper portion thereof. This publication describes that a gap between a slot sealing member which fixes the coil in a slot and the coil is used as an oil channel, such that oil is discharged from the cooling oil discharge port when an oil level of the cooling oil supplied from the cooling oil inlet port into the coil end cover and the oil channel rises and the cooling oil is supplied to an extent which fills the entire coil of the stator unit.
The cooling property of the stator coil end in the cooling system 26 for the rotating electric machine shown in FIG. 12 as described above requires further improvement. First, when configuring the stator coil end with the resin mold coil end 24, if the resin mold coil end 24 is formed by resin die forming, normally, the surface of the resin mold coil end 24 will be formed without pits and projections, and may therefore be too smooth. Therefore, there is a need for improvement to increase the surface area of the stator coil end side sufficiently to enable efficient exchange of heat between the stator coil end and the motor case 44, and also a possibility of improving the heat discharging property of the stator coil end. With such configuration, it is also possible that the cooling oil flowing on the surface of the resin mold coil end 24 may flow so quickly that, even though the cooling oil is supplied to the stator 22, heat is not effectively transferred to the cooling oil, and the cooling oil flowing over the surface of the resin may therefore not sufficiently cool the heated coils 16 (see FIG. 8) in the interior of the resin. Therefore, improvement of the heat discharging property of the stator coil end is also desirable.
When no device is made to the structure of an inner surface of the cover 36 opposing the resin mold coil end 24, the inner surface of the cover 36 may be formed as smooth, slippery surface of a high density material. Therefore, it is desirable to increase the surface area on the inner surface side of the cover 36, and also possible to further improve the heat discharging property of the stator coil end. Also, the cooling oil flowing over the inner surface of the cover 36 also tends to flow too quickly, and hence, even when the cooling oil which comes into contact with the stator coil end flows over the inner surface of the cover 36, sufficient heat may not be transferred from the cooling oil to the motor case 44, and the temperature of the coils 16 (see FIG. 8) may not be lowered sufficiently. From this point as well, there is need for improvement of the heat discharging property of the stator coil end. That is, there is an unmet need for improvement not only when the stator coil end is the resin mold coil end, but also when the coil end body 18 (see FIG. 8) is solidified using varnish or the like.
Improving the heat discharging property of the stator coil end by upsizing the rotating electric machine or by excessively increasing components of the rotating electric machine has been contemplated. However, with either of these approaches, undesirable increase in either or both of the weight of the rotating electric machine or the cost of manufacture of the rotating electric machine is brought.
In contrast, in the case of the motor disclosed in JP-A-2000-228843 described above, although the ribs are provided on the inner surface of the bracket opposed to the coil end, the portion between the adjacent ribs on the bracket may include the smooth, slippery surfaces and, in addition, the coil end is not resin-molded. Further, fixing separate ribs to the bracket undesirably increases the cost of manufacturing the motor. Therefore, improvement of the heat discharging property of the stator coil end is still desirable.
In the case of the rotating electric machine disclosed in JP-A-2005-73351 described above, because the cooling oil holding member used only for cooling the rotating electric machine is provided in the housing, the cost of manufacturing the rotating electric machine is undesirably increased. Therefore, improvement in terms of effective improvement of the heat discharging property of the stator coil end is further desired.
Also, in the case of the motor disclosed in JP-A-2005-354821 as described above, forming the notched portion for defining the coolant flow channel on the resin molded portion, and providing the coolant discharging hole penetrating through the resin molded portion both undesirably increase the manufacturing cost of the motor might be resulted. Therefore, improvement of the heat discharging property of the stator coil end is also desired in this respect.
In the case of the motor disclosed in JP-A1-2004/19468 as described above, providing the coil end cover which surrounds both end surfaces of the coil of the stator unit and the stator core undesirably increases the cost of manufacturing the motor. Improvement of the heat discharging property of the stator coil end is therefore also desired in this respect.